1. Technical Field
This invention relates generally to a method for forming a structure suitable for use as a core member, either by itself or as part of a multi-ply panel, and more particularly to a method for forming such a structure having a plurality of elongated passageways disposed parallel to the thickness of the core structure.
2. History of Related Art
Many structural arrangements have been proposed for use as a core member in laminated assemblies such as multi-ply panels having a surface ply bonded to at least one side of the core member. In particular, core structures formed of short elongated tubular segments arranged in parallel to the thickness of the core member have been found to provide exceptional resistance to compressive deformation and crush damage. However, because such structures comprise very large numbers of separate tubes or similar cell components, they have heretofore been difficult to assemble and manufacture economically. For example, U.S. Pat. No. 5,032,208, issued Jul. 16, 1991 to Horst Strauss describes a process for manufacturing a bundle of tubes by loading the tubes into a gutter having a moveable end wall. The end wall is then moved incrementally to expose one end of the tubes, which are then cut and the cut ends fused whereby adjacently disposed tube ends are joined together. The bundle is then moved to a position whereat a second cut can be made, then moved to a position at which a third cut can be made, and continued, seriatim, until the entire bundle has been cut into the desired number of cores. The Strauss process is not only cumbersome, allowing only one transverse cut and fusing operation at a time, but also is dependent upon precise, controlled movement of one end of the gutter while maintaining a desired alignment of the uncut tubes in the bundle.
In an earlier arrangement, a structural core panel construction is described in U.S. Pat. No. 2,477,852, issued Aug. 2, 1949 to C. E. Bacon, in which short tubular members are adhesively joined along their entire length. Alternatively, other shapes, such as corrugated strips may be precisely aligned and adhesively joined together along mating corrugations and then transversely cut to provide a core. In all of the arrangements taught in the Bacon structure, the individual components are adhesively joined along their entire length. This process is also cumbersome and time consuming, requiring that the adhesive be set before moving the structure for subsequent processing, such as applying a cover to the core member.
Recently, U.S. Pat. No. 5,683,782 issued Nov. 4, 1997 to Rainer Duchene describes a process for producing a honeycomb structure in which the individual components of the structure are coated with a heat-activated adhesive prior to assembly. After assembly, the adhesive is activated by a thermal treatment in which the individual components are bonded along their entire length. Thus, the Duchene process requires a precoating step prior to assembly and a separate thermal treatment prior to subsequent processing.
The present invention is directed to overcoming the problems set forth above. It is desirable to have a method for forming a structure suitable for use as a core in which a plurality of cores may be formed by simultaneous multiple cuts of a pre-assembled stack, or bundle, of components having internal passageways. It is also desirable to have such a structure that does not require adhesive joining of the separate components prior to forming into a core member. Furthermore, it is desirable to have a method by which a structure suitable for use as a core member can be formed without requiring a fixture having a moveable end wall by which only a single core member is formed before requiring movement of the assembled tubes to a subsequent position at which another core may be formed. Moreover, it is desirable to have a method for forming a plurality of cores simultaneously by which only selected open ends of the elongated members forming the core are fused together.
In accordance with one aspect of the present invention, a method of forming a structure suitable for use as a core member includes extruding a thermoplastic material into an elongated tubular shape, cutting the elongated tubular shape into a plurality of separate segments, and then aligning the separate segments in side-by-side relationship along their lengths. The aligned segments are then formed into a row having a preselected width, after which the rows are assembled one on top of another to form a stack of the rows. Thus the stack has a width substantially equal to the width of the rows of aligned segments, a depth substantially equal to the length of the segments, in the rows, and a height determined by the number of rows of aligned segments assembled in the stack. The stack of assembled rows is then cut in a direction transverse to the longitudinal axes of the aligned segments at a plurality of preselected spaced-apart distances, forming a plurality of separate cores each of which has a width and height substantially equal to the width and height of the stack and a thickness determined by the preselected distance between the transverse cuts. Simultaneously with cutting the stack of assembled rows, the aligned segments are fused to each other at at least one of the respective cut ends of the segments.
In other aspects of the present invention, the elongated tubular shape may have a hollow circular cross section, a hollow rectangular cross-section, a hollow triangular cross-section, a hollow hexagonal cross-section, or may have at least one transversely disposed internal wall forming a plurality of separate elongated hollow cells extending along the length of each of the tubular shapes. Other features of the method for forming a structure, in accordance with the present invention, include in the aligning step also moving the segments along a guideway having sidewalls that converge to a spaced-apart distance substantially equal to the length of the segments, and agitating at least one of the segments or the guideway during movement of the segments along the guideway. Other features of the method of forming a row of aligned segments also include fusing at least one of the cut ends of each of the aligned segments to the cut end of at least one adjacently disposed segment. The fusing of the cut ends may include heating the ends to a temperature sufficient to at least partially melt the cut ends of the aligned segments or mechanically bonding at least one of the cut ends of the aligned segments to the cut end of at least one adjacently disposed segment.
Yet another feature of the method of forming a structure, in accordance with the present invention, includes cutting the stack of assembled rows of aligned segments by making a plurality of simultaneous transverse cuts at spaced-apart distances along the longitudinal axes of the segments.
In accordance with another aspect of the present invention, the method of forming a structure suitable for use as a core member includes extruding a continuous thermoplastic sheet having a predefined width, at least one surface extending across the width of the sheet, and a plurality of parallel elongated passageways in which each of the elongated passageways has a longitudinal axis perpendicular to the width of the sheet. The extruded thermoplastic sheet is cut across its width to form a plurality of separate plates, each having a preselected length. The separate plates are assembled one on top of another to form a stack of plates in which the elongated passageways in each plate are arranged in a common parallel direction perpendicular to the width of the stack. The stack has a width substantially equal to the width of the plates, a depth substantially equal to the preselected length of the plates, and a height determined by the number of plates assembled in the stack. The stack of assembled plates is then cut in a direction transverse to the longitudinal axes of the elongated passageways at a plurality of preselected spaced-apart distances along the axes. The cutting of the stack in this manner forms a plurality of separate structures, each having a width and height substantially equal to the width and height of the stack and a thickness determined by the preselected distance between the transverse cuts through the stack. The method further includes simultaneously fusing adjacently disposed plates to each other at at least one of the respective cut ends of the plates, simultaneously with cutting of the stack.
Other features of the method for forming a structure in accordance with the method immediately set forth above includes the elongated passageways having a selected one of a number of cross sections, including the cross-sectional shapes enumerated above. Furthermore, the elongated passageways may be at least partially formed by a base wall having a first side defined by a surface extending across the width of the thermoplastic sheet, and a plurality of spaced-apart parallel walls extending from a second side of the base wall in a direction normal to the base wall. Also, the elongated passageways may be defined by a plurality of adjacently disposed U-shaped channels wherein the bottoms of the U-shaped channels define a surface extending across the width of the thermoplastic sheet. In yet another arrangement, the surface extending across the width of the thermoplastic sheet may be defined by one side of a serpentine wall, and the elongated passageways defined by alternating convex and concave curved portions on respective sides of the serpentine wall. Other features of the method of forming a structure, as set forth above, include the step of simultaneously fusing adjacently disposed plates to each other by heating at least one of the cut ends of each of the plates to a temperature sufficient to at least partially melt the respective cut ends whereupon, on cooling, the cut ends are mutually fused together.
Other features of assembling of the plates includes the stacking of the plates in a structure having openings provided therein that are adapted to provide access to the stack of plates for the purpose of wrapping at least one band of a heat-shrinkable plastic material around the stack. Still other features of the method include cutting the stack of assembled plates by making a plurality of simultaneous cuts at spaced-apart distances in a direction along the longitudinal axes of the passageways of the plates.
In yet another aspect of the present invention, a method of forming a structure suitable for use as a core member includes extruding a thermoplastic material into an elongated tubular shape, cutting the elongated tubular shape into a plurality of separate segments and aligning the separate segments in side-by-side relationship along their preselected lengths. The plurality of aligned separate segments is then shrink-wrapped, with the shrink wrapping surrounding the aligned separate segment and forming a bundle of shrink-wrapped segments. The shrink-wrap bundle is then cut in a direction transverse to the longitudinal axes of the segments, thereby forming a plurality of separate shrink-wrapped structures, each of having a thickness determined by the preselected distances between the transverse cuts. At least one of the cut ends of the respective segments is simultaneously fused with an adjacently disposed aligned segment in the bundle during the cutting operation. Other features of the immediately above-described method of forming a structure include the elongated tubes having a cross section such as those previously described.
In still another aspect of the present invention, a method of forming a structure suitable for use as a core member includes extruding a thermoplastic material into an elongated tubular shape, cutting the elongated tubular shape into a plurality of separate segments, and aligning a plurality of separate segments in side-by-side relationship along their lengths. The aligned separate segments are then deposited into a consumable container formed of a material that is capable of being cut by a thermal apparatus. The consumable container and the aligned segments deposited within the container are cut in a direction transverse to the longitudinal axes of the aligned segments at a plurality of preselected spaced-apart distances along the longitudinal axes of the segments. This forms a plurality of separate cores, each having a thickness determined by the preselected distance along the transverse cuts. Simultaneously with cutting through the deposited separate segments and the consumable container, adjacently disposed aligned segments are simultaneously fused to each other at at least one of the cut ends of the respective segments.
Other features of the method of forming a structure, in accordance with the immediately above description, includes the consumable container being formed of expanded polystyrene. Additional features include the consumable container being disposed within a structure having openings provided therein that are adapted to provide access to the container containing the plurality of segments for the purpose of wrapping at least one band of a plastic material around the consumable container.
Still other methods include cutting of the deposited separate segments and the consumable container by making a plurality of simultaneous cuts, desirably by heated wires, at spaced-apart distances along the longitudinal axes of the segments.
In accordance with another aspect of the present invention, a member suitable for use as a core has a pair of spaced-apart surfaces defining the thickness of the member. The member also has a plurality of adjacently disposed rows of a thermoplastic sheet structure, with the rows being disposed in a direction parallel with the thickness of the member. Each row of the thermoplastic sheet structures have a defined width, at least one surface extending across the width, and a plurality of elongated passageways disposed in parallel relationship with the aforementioned surface and with each other. Each of the elongated passageways have a longitudinal axis oriented perpendicular to the direction of the width of the sheet. A portion of the at least one surface is fused with a portion of the at least one surface of an adjacently disposed row of the thermoplastic sheet structures.
Other features of the member suitable for use as a core include the fused portions of the respective surfaces being positioned at at least one of the pair of spaced-apart surfaces defining the thickness of the member. Also, the elongated passageways may have any of a number of hollow cross sections, including rectangular, triangular, circular, hexagonal, or may have at least one transversely disposed internal wall which forms a plurality of separate elongated hollow cells extending along the length of each of the passageways.